In vehicles at present time, reduction of exhaust gas materials such as carbon monoxide (CO), carbon hydride (HC) and nitrogen oxide (NOx) included in exhaust gas from the vehicles is required in terms of environmental conservation. Further, reduction of exhaust amount of carbon dioxide (CO2) is a serial problem, and improvement of fuel consumption is also required for this purpose. To respond to these requirements, a fuel injection control apparatus to inject fuel to an internal combustion engine is developed and improved.
Generally, as a method for supplying fuel to a combustion chamber of an internal combustion engine, direct injection method to directly inject fuel to the combustion chamber with a fuel injection valve provided in a cylinder head of the combustion chamber, and a multi-point injection method to inject fuel into an intake port connected to the combustion chamber with a fuel injection valve provided in the intake port. The present invention relates to the latter method, multi point injection method.
In the multi point injection method, since the intake port is provided with the fuel injection valve, it is necessary to supply fuel, injected from the fuel injection valve, on an air flow, to the combustion chamber. For example, Japanese Patent Laid open No. 2003-83126 (Patent Literature 1) discloses the following technique.
That is, a fuel injection valve is provided toward an intake valve and a flow velocity sensor to detect flow velocity in the intake port is provided in the intake port. Upon cooling, to avoid attachment of fuel to the intake valve, fuel is injected during an intake stroke where the intake valve is open. In the internal combustion engine, since gas reverse flow occurs from the combustion chamber immediately after the valve opening of the intake valve, a crank angle upon termination of reverse flow is obtained with the flow velocity sensor, and fuel injection is performed with the reverse flow termination time possible to supply the injected fuel, on the air flow, to the combustion chamber.
In a reciprocating internal combustion engine which performs intermittent intake operation, an intake pulse occurs due to propagation of pressure wave in the intake port. The form of the intake pulse has different variants in accordance with the number of cylinders forming the internal combustion engine, intake/exhaust valve opening/closing timing, the number of engine revolutions, load and the like.
In the above described Patent Literature 1, the crank angle upon termination of reverse flow in the intake port is obtained with the flow velocity sensor provided in the intake port, and injection is performed at the time of the reverse flow termination as the injection start time. In this patent literature 1, the direction of the gas in the intake port is taken into consideration, however, there is no consideration about the level of gas flow velocity in the intake port.
In a status where the intake pulse occurs, the level of the gas flow velocity as well as the direction of the gas flow velocity changes in the intake port. The level of gas flow velocity in the intake port has much influence on the behavior of fuel injected at the intake stroke. When the fuel is injected at timing where the level of the gas flow velocity in the intake port is inappropriate, the fuel consumption may be degraded or the exhaust emission may be increased.
The present invention provides a fuel injection control apparatus for an internal combustion engine capable of, upon intake stroke injection, injecting fuel at optimum timing in correspondence with the level of gas flow velocity in an intake port.